Thanks ..... well it seems you can always remove 2 clues from a row/box of 9.Usually a few 6plus12s are valid.suppose that if there isnt a 6plus 12 then my technique wont find them .....hmmmmmfwiw - it is always possible to " fix" 2 of the 12 clues ..... but we are not close to an exaustive search just yet !

+---+---+---+|123|456|789||.8.|...|..1||...|..7|..5|+---+---+---+|7..|..1|..4||...|...|..8||...|.3.|..2|+---+---+---+|.5.|.8.|..3||...|...|..7||4..|...|..6|+---+---+---+ a 17plus8 was found !!!! [betters the 17plus9]

This probably the best we can do with a full complement of clues on 2 adjacent edgesSo this arrangement of 64 cells must have at least 8 clues C

Last edited by coloin on Tue Aug 06, 2013 3:13 am, edited 2 times in total.

1234567898.......1....3...........4........3.9....1....45...........98..........6#[several other puzzles within{+5}]123456789........16............91........5...2.....3....9.......8..3.......2..6..#[no other puzzles within {+5}]

they are within {+7} of each other which is probably not unexpected. The 2nd puzzle is more remote .....